The invention relates to a transflective display device comprising an electro-optical material between a first transparent substrate and a second transparent substrate, with an illumination device on the side of the second substrate.
Such display devices, notably liquid crystal display devices, find an increasingly wider application in, for example, portable telephones, automotive uses, etc.
A transflective display device usually comprises a transflector which, when used in transmission (referred to as the xe2x80x9cnight view modexe2x80x9d) partly transmits light from a backlight placed behind the display device or, when used in reflection (referred to as the xe2x80x9cdaytime view modexe2x80x9d) reflects incident light.
In the common transflectors, the reflection is approximately 65% of the incident light, while only approximately 35% of the light from the backlight is passed by the transflector. This is at the expense of the brightness, unless a brighter light source is chosen, which requires extra energy and reduces the lifetime of the battery. An increase of the transmission in the xe2x80x9cnight view modexe2x80x9d is at the expense of brightness and contrast in the xe2x80x9cdaytime view modexe2x80x9d.
It is, inter alia, an object of the invention to find a solution to the above-mentioned problem. To this end, a transflective display device according to the invention is characterized in that a switchable mirror is arranged between the illumination device and the electro-optical material, which mirror is switchable between a transparent state and a state reflecting light in the direction of the layer of electro-optical material.
A first embodiment of a transflective display device according to the invention is characterized in that the mirror is provided with a switchable layer comprising a trivalent metal which can form a hydride with hydrogen, and the switchable layer is reversibly switchable between a reflecting state and a transparent state by exchange of hydrogen.
The switchable layer preferably also comprises magnesium which can form hydrides. It has been found that a reflection of at least 75% and, in some cases, of 85% to 90% is realized with such layers, while these layers are switchable (within 1 to 10 sec) to a transparent state in which 80% to 90% of the light is transmitted. If necessary, the switchable layer is provided with a catalytically active layer comprising at least one metal of the group of palladium, platinum, cobalt and nickel.
A second embodiment of a transflective display device according to the invention is characterized in that the switchable layer is in contact with a liquid electrolyte, a gel electrolyte or a solid-state electrolyte. Examples are 1 molar KOH in water, 1 molar trifluoroacetic acid in symmetric collidine and cerium oxide (CeO2).
A particularly advantageous embodiment causes the switchable mirror and the illumination device to switch in a coupled way (for example, simultaneously).
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.